Eukaryotic cells have evolved a novel endoplasmic reticulum (ER) to nucleus signaling pathway, the unfolded protein response (UPR) to respond to condtions of ER stress. UPR induction is initiated by the activation of Ire1, an ER-resident kinase and endoribonuclease. UPR dysregulation is implicated in viral infection, Alzheimer's disease, and with insulin resistance and type 2 diabetes. This proposal describes experiments designed to understand the molecular mechanisms of Ire1 signal generation in the UPR signaling pathway using small molecule inhibitors. A cell-based assay in combination with high throughput technologies will be used to screen libraries of thousands of small molecules for Ire1 inhibition. These inhibitors will be used as tools to probe their effects on UPR signal transduction and downstream signaling cascades. In vitro biochemical experiments with purified Ire1, using a combination of biochemistry and x-ray crystallography, will be initiated to understand the structure/function relationships of Ire signaling as well as the mode of inhibition of these small molecules at atomic resolution. Understanding the mechanisms of Ire1 signaling will facilitate the modulation of UPR signalling thus aiding in the treatment of UPR relateddiseases.